Phenothiazine derivatives

ABSTRACT

A composition having the formula ##STR1## wherein n has an average value of one to about five, is disclosed for use in reducing or eliminating the formation of reactor scale during the polymerization of vinyl chloride and comonomers. The composition is prepared by reacting phenothiazine with formaldehyde in the presence of a liquid diluent that is a solvent for the phenothiazine, but a non-solvent for the dimer of phenothiazine and formaldehyde. The process of the invention is preferably conducted in the presence of a strong acid catalyst. The formaldehyde is preferably added slowly to the reaction mixture over the course of the reaction. The product can be filtered and dried.

BACKGROUND OF INVENTION AND INFORMATION DISCLOSURE STATEMENT

1. Field of Invention

In the manufacture of polyvinyl chloride and copolymers of vinylchloride, the resin tends to adhere to the reactor walls during thepolymerization of the vinyl chloride and comonomers. The buildup ofscale on the reactor walls interferes with heat transfer, it consumesvaluable monomer which is lost to the final product, and it results inthe increase in waste product that must be disposed of safely.

2. Prior Art

U.S. Pat. No. 2,415,252 describes the preparation of phenothiazinederivatives by reacting phenothiazine with formaldehyde and an alcoholunder conditions that produce a modified phenothiazine that has attachedthereto a methylene group and an alkoxy group. The compounds and theirsolutions in oil are said to be useful for pharmaceutical, veterinaryand pest-control purposes.

U.S. Pat. No. 2,528,092 describes the reaction of phenothiazine withformaldehyde and N-dimethylaniline. The resulting compound is useful asan antioxidant for mineral oil lubricants.

U.S. Pat. No. 4,465,881 describes N,N'-dimers of phenothiazine or asubstituted phenothiazine. The compounds result from the linkage of twophenothiazine molecules through their N groups. These dimers areprepared by heating phenothiazine in the presence of an organicperoxide. These dimers are disclosed to be useful to stabilize vinylaromatic compounds such as styrene and substituted styrenes againstundesired polymerization.

U.S. Pat. No. 4,529,500 discloses the use of the N,N'-dimer ofphenothiazine or a substituted phenothiazine to protect hydrocarbonprocessing equipment against fouling during the processing ofhydrocarbons at elevated temperatures.

An article published in the USSR by Romanovich and coauthors andreported in Chemical Abstracts as 98:144251d, describes the reaction ofphenothiazine and formaldehyde under conditions that favor theproduction of hardened products wherein reaction appears to take placeat the nitrogen group of the phenothiazine, ultimately resulting in theformation of cross-linked products of relatively high molecular weight.

In U.S. Pat. No. 4,229,510, a polymer material is formed from asubstituted phenothiazine wherein the nitrogen group is substituted withan alkyl group. It appears that reaction with formaldehyde occursbetween the phenyl groups and formaldehyde. The resulting product hasthe nitrogen group blocked with the alkyl group of the startingmaterial. The resulting products are reported to have photoconductiveproperties.

OBJECTS OF INVENTION

It is an object of the present invention to provide a novel compositionof matter and process for making the composition.

It is a further object of the invention to provide a new compositionthat functions to prevent or reduce reactor wall fouling or scaledeposits, as well as flocculated material, during polymerization ofvinyl chloride and comonomers.

Another object is to provide a novel polymerization inhibitor.

SUMMARY OF THE INVENTION

In accordance with this invention there are provided novel compoundswhich have the formula ##STR2## The preferred compound is 3,3'-methylenebis(phenothiazine). The novel compounds are produced by condensingphenothiazine with formaldehyde.

Also provided in accordance with the invention are reaction productscomprising the above-mentioned bis(phenothiazine) compounds and minoramounts of higher condensation products of phenothiazine andformaldehyde.

Further in accordance with the invention there is provided a novelprocess whereby phenothiazine is reacted with formaldehyde in thepresence of a liquid diluent that is a solvent for the phenothiazine,but a non-solvent for the dimer of phenothiazine and formaldehyde andhigher oligomers of phenothiazine and formaldehyde.

The process of the invention is preferably conducted in the presence ofa strong acid catalyst. The formaldehyde is preferably added slowly tothe reaction mixture over the course of the reaction. The product can befiltered and dried.

EMBODIMENTS OF THE INVENTION

The invention involves reaction products of the compound phenothiazinewhich has the formula ##STR3## This compound is currently used in animaldisease control, in pharmaceutical applications, such as againstpinworms in animals.

In the preparation of the compositions of the invention, thephenothiazine is reacted with formaldehyde. The molar ratio offormaldehyde to phenothiazine is generally in the range of about 0.1 toless than 1, preferably in the range of about 0.4 to less than 1, andmore preferably about 0.5.

Diluents for the reaction mixture of the invention are liquids thatdissolve phenothiazine, but which are not solvents for the dimer ofphenothiazine and formaldehyde and higher oligomers of phenothiazine andformaldehyde. Thus, in the course of the reaction, as the dimer andhigher oligomers of the phenothiazine are formed, such dimers and higheroligomers precipitate from the diluent and can be removed from thereaction mixture.

Suitable diluents include non-polar solvents such as tetrahydrofuran(THF), dimethylformamide (DMF), cyclohexanone and dimethylsulfoxide(DMSO).

Suitable polar diluents include alcohols, preferably those alcoholshaving one to five carbon atoms, although higher alcohols up to 10carbons can be used.

With respect to the reaction of the invention, mixtures of polar andnonpolar solvents are found to be best suited to perform the function ofdissolving the monomer but precipitating the dimer and higher oligomers.It is found that the solubility function is important in determining thestructure of the product of the invention. Thus, if too powerful asolvent is employed, the dimer and higher oligomers do not precipitateand too high a molecular weight is achieved. If, on the other hand, thesolvent is too poor, the monomer has difficulty dissolving and beingavailable for the reaction with the formaldehyde to form the reactionproduct.

The diluent is employed in the reaction mixture such that thephenothiazine is present in an amount from about one or two weightpercent up to about 25 weight percent, preferably up to about 10 weightpercent of the diluent. The reaction product should be sufficientlydilute so that it can be filtered to remove the solvent from theproduct.

The weight ratio of polar to non-polar solvent is generally in the rangeof about 0.1 to 10, preferably about 0.5 to 2, and still more preferablyabout 1 to 1.

Either acidic or alkaline compounds can be employed as catalysts for thereaction. However, acid compounds are preferred, and of these the strongacids are more preferred. The preferred compounds include hydrochloricacid, sulfuric acid, nitric acid and phosphoric acid. Suitable causticcompounds include sodium hydroxide and other alkali metal hydroxides.

In the process of the invention, the formaldehyde is slowly added to themixture of diluent and phenothiazine so that there is an orderlyreaction to form the dimer and higher oligomers, and subsequentprecipitation of the dimers and oligomers from the reaction mixture.

The preferred reaction temperature is in the range of room temperatureto the reflux temperature of the lowest boiling diluent, preferablyabout 60 to 80 degrees Celsius.

The reaction mixture is removed from the reaction vessel and filtered byconventional means. Suitable filter media include paper and cloth, suchas nylon cloth.

The filtered product is dried at a temperature in the range of aboutroom temperature up to the melting point of the composition of theinvention, preferably at a temperature of about 50 to 100 degreesCelsius.

The reaction product of the invention generally comprises a mixture ofthe following components.

    ______________________________________                                        Component       Weight Percent                                                ______________________________________                                        Phenothiazine                                                                 Monomer         1 to 10                                                       Dimer           70 to 85                                                      Trimer          5 to 15                                                       Higher Oligomers                                                                              5 to 10                                                       ______________________________________                                    

The reaction product generally has the formula ##STR4## wherein n has anaverage value of about 1 to about 5, preferably 1 to about 2, and morepreferably 1 to about 1.5. The composition is composed of a mixture ofindividual compounds of the formula wherein n is an integer from 1 toabout 10, preferably from 1 to about 5.

The reaction mixture can be processed to change the relative ratios ofthe foregoing components. Thus, the unreacted monomer can be removedfrom the reaction mixture by methanol extraction down to about 0.5weight percent or less of unreacted monomer.

The dimer can be separated from the trimer and higher oligomer materialsby a series of extractions with suitable solvents.

The conversion of the phenothiazine to dimer and higher oligomer isgenerally in the range of about 75 to 90 percent.

The dimer of the invention or the reaction products including the dimerare utilized as follows in the reduction or elimination of scale andflocculated material in a reaction vessel and components such as anagitator used for the polymerization of vinyl chloride. The compositionsof the invention are also useful in the polymerization of vinyl chloridewith ethylenically unsaturated comonomers in a proportion of up to about80 mole percent comonomers. Such comonomers include vinyl acetate, andother ethylenically unsaturated monomers that are well known in the art.

The dimer alone or together with higher oligomers is dissolved in asuitable solvent such as THF in a proportion of about 0.3 to about 1weight percent. The resulting solutions are then brushed or sprayed onthe reactor walls, on the reactor agitator, and inside the reactor head.The polymerization reaction mixture is inhibited from formingundesirable scale on the reactor components. Other solvents that can beemployed in the application of the solutions to the reactor componentsinclude DMF, cyclohexanone and DMSO.

The composition of the invention can also be added directly to thepolymerization reaction mixture, generally in a proportion of about0.0001 to about 0.01 weight percent solids, preferably about 0.001weight percent solids based on the weight of vinyl chloride andcomonomers. The composition of the invention can be added to thepolymerization zone as dry solid or in solution in the foregoingsolvents. The composition can also be added in the wet cake form afterfiltering, but before drying in the manufacturing process.

The dimer of the invention or the reaction products including the dimerare also useful in inhibiting the polymerization of monomers such asvinyl chloride or in shortstopping the polymerization of such monomers.

EXAMPLES

In the following examples and throughout the specification and claims,parts are by weight and temperatures are in degrees Celsius, unlessindicated otherwise.

EXAMPLE 1

2.0 grams of phenothiazine were dissolved in 8.0 cc of THF. 2.0 cc ofconcentrated HCl and 1.6 cc of 37 weight percent formaldehyde solutionwere added to 12.0 cc of methanol. The methanol solution was addedslowly with stirring to the THF solution at room temperature. Themixture darkened slightly and became warm. After 5 minutes of stirring,the mixture became cloudy and a precipitate formed. After stirring for 1hour, the mixture was filtered on a Buchner funnel. The filter cake wasslurried with dilute sodium carbonate to remove HCl and again filteredand washed several times with deionized water. After drying for an hourat 60° C., the product was mostly soluble in THF. The soluble portionwas tested for reactor buildup control, and analyzed by gel permeationchromatography (GPC) and nuclear magnetic resonance (NMR).

The NMR analysis showed that the major reaction product in the THFsoluble portion had the following structure ##STR5##

The GPC analysis showed that the soluble portion contained about 80percent of the dimer of phenothiazine and formaldehyde.

The GPC data coupled with other analyses showed that the solvent-washedproduct of the invention contained 5 percent phenothiazine, 78 percentdimer, and 17 percent higher oligomers such as trimer, tetramer andhigher oligomers.

The soluble portion was found to inhibit reactor fouling duringpolymerization of vinyl chloride.

EXAMPLE 2

4.0 grams of phenothiazine were dissolved at room temperature withstirring in 8.0 cc of tetrahydrofuran. A solution of 1.0 cc ofconcentrated hydrochloric acid and 0.4 cc of 37 weight percentformaldehyde solution in 8.0 cc of methanol was added slowly withcontinued stirring. The solution darkened and after 5 minutes,precipitation began and the mixture rapidly became a thin slurry. At5-minute intervals, 0.4 cc increments of 37 weight percent formaldehydesolution were added until the mixture contained a total of 2.0 cc of 37weight percent formaldehyde solution. After 2 hours, the mixture hadthickened considerably and 4.0 cc of methanol were added, followed byanother 4.0 cc after 3 hours. After 5 hours, the slurry was filtered andwashed with a 2/1 mixture by volume of methanol and tetrahydrofurancontaining ammonium hydroxide to remove unreacted phenothiazine and toneutralize the hydrochloric acid. The dried product was analyzed byinfrared, gel permeation chromatography and nuclear magnetic resonanceand found to be 80 weight percent 3,3'-methylene bis(phenothiazine)along with higher oligomers. The infrared analysis showed a strongsecondary amine band. The bis(phenothiazine) and higher oligomers aresoluble in tetrahydrofuran, dimethylformamide, cyclohexanone anddimethylsulfoxide.

EXAMPLE 3

2.0 grams of phenothiazine, 0.3 grams of paraformaldehyde and 1.0 cc ofconcentrated hydrochloric acid were added to 18.0 cc of methanol and 4.0cc of tetrahydrofuran at reflux temperature. Precipitation of productbegan immediately, and stirring was continued for one-half hour atreflux. The precipitated product was filtered and dried. The driedproduct was soluble in dimethylformamide. Infrared analysis of theproduct showed a strong secondary amine band.

EXAMPLE 4

4.0 grams of phenothiazine was dissolved in 10 cc of dimethylformamide.4.0 cc of concentrated hydrochloric acid and 0.4 cc of 37% formaldehydesolution in 10 cc of methanol were added with stirring. Precipitationbegan immediately and four more 0.4 cc increments of 37 weight percentformaldehyde solution were added at 2 minute intervals with stirringcontinued for one half hour. Solid precipitated product was filtered onpaper and was washed with 2/1 parts by volume of methanol/THF solutioncontaining ammonium hydroxide to remove hydrochloric acid and excessphenothiazine. 51 percent yield of dried product was obtained which wassoluble in 50/50 parts by volume DMF/THF solution to the extent of 10weight percent. Infrared analysis of the product showed a strongsecondary amine band.

The foregoing examples demonstrate that the desired product is obtainedby early precipitation from the reaction medium. The product isprevented from further reacting with formaldehyde to form undesirable,insoluble cross-linked polymer.

EXAMPLE 5 (Control)

4.0 grams of phenothiazine were dissolved in 10 cc of dimethylformamidewith stirring and heating to 65° C. Then, 1.0 gram of paraformaldehydewas added, followed by 1.0 cc of concentrated hydrochloric acid. Aninsoluble gel formed. The solvent was removed. The resulting product wasa hard resinous material that was insoluble in dimethyformamide. IRanalysis of this product showed no evidence of a secondary amine group.This example showed the importance of controlling reaction conditions inobtaining the desired product, and specifically the effects of higherformaldehyde concentration, high temperature and use of too strong astrong solvent.

EXAMPLE 6

A PVC suspension polymerization process formulated to yield high scalebuildup on the reactor walls was carried out at 60° C. in a stainlesssteel reactor. In the preparation for the polymerization process, thereactor walls, stainless steel agitator and the reactor head were coatedwith a 0.5 weight percent solution in tetrahydrofuran of product made inaccordance with Example 2. The coating was air dried.

The following formulation was used:

    ______________________________________                                        Component               Grams                                                 ______________________________________                                        Vinyl Chloride          400                                                   Deionized Water         525                                                   Hydroxypropyl Methylcellulose                                                                         1.10                                                  Partially Hydrolyzed Polyvinyl Acetate                                                                0.5                                                   2,2'-azobis (2,4 dimethylvaleronitrile)                                                               0.10                                                  ______________________________________                                    

A control polymerization was carried out with the same polymerizationformulation, but with no coating employed.

Buildup on all surfaces of the reactor amounted to 40.0 grams for thecontrol polymerization, and 17.0 grams for the coated reactor andcomponents.

EXAMPLE 7

A PVC emulsion polymerization known to yield moderately high reactorbuildup was carried out at 50° C. in a glass reactor with a stainlesssteel agitator. The following polymerization formulation was used:

    ______________________________________                                                               Grams                                                  ______________________________________                                        Vinyl Chloride           300                                                  Deionized Water          600                                                  Potassium Persulfate     0.2                                                  Sodium Metabisulfite     0.04                                                 Sodium Bicarbonate       0.2                                                  Seed Latex (30 weight percent total solids)                                                            4.8                                                  Sodium Lauryl Sulfate    2.25*                                                ______________________________________                                         *Continuously added over 8 hours in a 3.2 weight percent solution in wate                                                                              

12.5 ppm (based on the weight of vinyl chloride) of product made inaccordance with Example 2 was added to the reactor contents.

A control polymerization was carried out with the same polymerizationformulation, but with no product according to Example 2 employed in theprocess.

In the control reaction, buildup on the metal surfaces and the glassbowl amounted to 5.5 grams together with 10.4 grams of flocculatedmaterial. Buildup in the reactor containing the product made inaccordance with Example 2 was negligible with 2.5 grams of flocculatedmaterial.

EXAMPLE 8

A PVC microsuspension polymerization known to yield high reactor buildupwas carried out at 55° C. In preparation for the polymerization process,the agitator was coated with a 2 weight percent solution intetrahydrofuran of product made in accordance with Example 2. Thefollowing polymerization formulation was used:

    ______________________________________                                                        Grams                                                         ______________________________________                                        Vinyl Chloride    400                                                         Deionized Water   370                                                         Sodium Lauryl Sulfate                                                                           4.0                                                         Mixed Fatty Alcohols                                                                            5.0                                                         Lauroyl Peroxide  0.20                                                        ______________________________________                                    

In order to provide a high buildup, homogenization of the formulationwas carried out for 21/2 minutes at low pressure before polymerization.

A control polymerization was carried out with no coating on theagitator.

Buildup on all surfaces of the control reactor amounted to 8.0 gramstogether with 5.0 grams of flocculated material. Buildup in the reactorwith the agitator coated was negligible together with 1.0 grams offlocculated material.

EXAMPLE 9

A PVC mass polymerization was carried out at 50° C. in a glass reactorwith a stainless steel agitator with 17 ppm of the product prepared inaccordance with Example 1 added to the reactor contents. The followingformulation was used:

    ______________________________________                                        Component             Grams                                                   ______________________________________                                        Vinyl Chloride        300                                                     Di-Sec.Butyl Peroxydicarbonate                                                                      0.75                                                    Span 60 Surfactant    1.5                                                     ______________________________________                                    

100 grams of 0.1% methocel solution was used to wash the Di-Sec.ButylPeroxydicarbonate and span 60 into the reactor. The reaction was carriedout to 28 percent conversion and stopped.

A control polymerization was carried out with no product in accordancewith Example 2.

The buildup on the metal surfaces and the glass bowl for the controlamounted to 1.25 grams. Buildup in the reactor containing the productfrom Example 1 was 0.24 grams.

The product of Example 3 prevented buildup and flocculated material inthe same fashion as product material from Example 2. Product fromControl Example 5 was insoluble in solvents such as THF, and wascompletely unsuitable for coating reactor components.

EXAMPLE 10

The effect of phenothiazine/formaldehyde condensation product preparedin accordance with Example 1 on stopping conversion of vinyl chloridemonomer to polymer was examined by carrying out polymerization asdescribed in Example 7. After 6 hours at reaction temperature, 0.06 PHMof condensation product prepared in accordance with Example 1 was addedas 10 weight percent solution in 50/50 ratio by volume of DMF/THF. Thebatch was vented after 18 hours, then cooled, and the percent conversionof monomer to polymer was determined.

EXAMPLE 11

A control polymerization with the addition of 0.06 PHM of Bisphenol A, aknown polymerization inhibitor, was carried out in the same way asExample 10.

EXAMPLE 12

A control polymerization with no polymerization inhibitor added wascarried out in the same way as Example 10.

Table I compares the effects on monomer conversion of procedures used inExamples 10, 11 and 12.

                  TABLE I                                                         ______________________________________                                        MONOMER CONVERSION IN 18 HOURS                                                ______________________________________                                               Example 10     28%                                                            Example 11     52.5%                                                          Example 12     76%                                                     ______________________________________                                    

We claim:
 1. A compound having the formula ##STR6##
 2. 3,3'-methylenebis(phenothiazine).
 3. A composition having the formula ##STR7## whereinn has an average value of about one to about five.
 4. The composition ofclaim 3 wherein n has an average value of about one to about two.
 5. Thecomposition of claim 3 having about 70 to about 85 weight percent of3,3'-methylene bis(phenothiazine).
 6. A solution of the compound ofclaim 1 dissolved in a solvent.
 7. A solution of the composition ofclaim 3 dissolved in a solvent selected from tetrahydrofuran,dimethylformamide, cyclohexanone and dimethylsulfoxide.